Parallax correction circuit



v XR 298249692 I y ff? f5 i? Feb. 25, 1958 N. s. Fox 2,324,692

PARALLAX CORRECTION CIRCUIT Filed sept. 28, 1954 en nl `sme 4sERvo T- Cosme i COMPUTER Z 25 5 /37 42 I9 ey 2 Y ehr sanvo I ee l SINE J Cosma L46 COMPUTER SERVO r AZIMUTH ANGLE AZMUTH ANGLE MAGNITUDE SWITCHES ELEVATlGN ANGLE QUADRAHT SWITCH AZIMUTH RANGE ELEVATION 78 N ANGLE ANGLE 2 INVENTOR.

NELSON S. FOX

www 772 dwf@ A TTRWEY rates ite {Granted under litle 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Liovernment for governmental purposes without the payment of any royalty thereon.

t ne present invention relates to a new and useful parallax correction circuit for use in the correction of data to be used at a point physically separated from the point where the data was derived. More specilically, the parallax correction circuit is applicable to systems wherein an object such as a gun, searchlight or antenna is to be directed toward a particular location in space under the control of data dehning such position in space which is derived at some point other than that at which the controlled object is located. A common example of such equipment would be an installation where a plurality of directional antennae are controlled from a single director station physically separted from one or more of the antennae. lt will be readily apparent that data defining the position of the object with respect to the location of the director will not be correct for any other point and that parallax correction factors must be added.

The present parallax correction circuit is intended for use with a known control-system which utilizes input data defining the position of the object in terms of three dimensional rectangular coordinates. The correction circuit is intended to operate to set up from polar coordinate information the proper correction factors in terms of such rectangular coordinate data as to the difference in location of the control and director installations.

A principal object of the invention is to provide a circuit for the production of parallax correction data.

Another object of the invention is to provide a paral lax correction circuit which may be set up on the basis o polar coordinate information to produce rectangular coordinate correction data.

A still further object of the invention is to provide an electrical parallax correction circuit which operates upon a voltage ratio principle to deliver the required correction voltages.

These and other objects of the invention will become more apparent as the invention becomes better understood from the following detailed description and drawings wherein:

Fig. l is a schematic circuit largely in block diagram form of a known control system with which the improved parallax correction circuit is useful,

Fig. 2 is a schematic diagram of the parallax correction circuit itself,

Fig. 3 is a an explanatory three dimensional diagram showing the relative locations of the control station, the director station and the remote object to illustrate the type of problem to which the parallax circuit according to the invention is applicable.

Turning rst to Fig. l, the control system to which the parallax correction circuit is to be applied will be described. A plurality of summing amplifiers l1, 13 and 15 are provided. The amplifiers are provided with main input terminals i7, 19 and 21 respectively and auxiliary or correction input terminals 23, 25 and 27 respectively.

C 2524,5922 Patented F el). 25, 1958 The amplifiers are of a type well known in the art and are such as to provide an output voltage proportional to the algebraic 'sum ot' the two input voltages applied thereto.

'lne outputs of ampliers 11 and 13 are connected as indicated to a sine-cosine computer 29. The output of amplin'er 15 and an electrical output ot computer 29 are connected as indicated to a similar sine-Cosme computer 31. An electrical output of the computer 29 is connected to an azimuth servo motor 35. A lrst electrical output of the computer 3l is connected to an elevation servo motor 37 and a further electrical output ot the computer 31 is connected to a range servo motor 39.

The sine-cosine computers 29 and 31 form no part of the present invention and hence have not been specifically illustrated. They are of a type well known in the art and are described in the Radiation Laboratory Series, volume 2l, Electronic instruments, pages l60l64, published by McGraw-Hill Book Co. lnc., New York, N. Y., in i948.

rlhe system of Fig. 1 is intended to solve a problem wherein the position ot` an object has been located with respect to a director station. The director (not shown) commonly used develops three output voltages representative of the rectangular coordinates in three dimensions of the position of an object with respect to the location ot the director. The coordinate system is set up by three planes designated the X, Y and Z planes. These planes are located in space at right angles to one another with a common point of intersection at the location of the director.

If the control system to be used were to be located at the position of the director the three coordinate voltages could be utilized directly. As has been previously indicated however, it' the control system is not located at the director, correction for parallax must be made.

The system of Fig. l is set up with three input amplifiers 11, 13 and l5 for the three coordinate voltages from the director. These voltages are applied to the main input terminals 17, 19 and 21 of the amplifiers. Amplifiers 11, 13 and l5 are also provided with auxiliary input ter minals 23, 25 and 27, and each amplifier is so constructed as to develop an output voltage proportional to the algebraic sum of the voltages applied to its main and auxiliary terminals. The coordinate voltages from the director are applied to the main input terminals and correction voltages developed by the novel circuit according to this invention are applied to the auxiliary terminals. Three parallax corrected output voltages, ex, ey and ez are then obtained from the output of the amplifiers 11, 13 and 15. These voltages are representative of the true rectangular coordinates of the remote object with respect to the control station where they are to be utilized. These corrected coordinate voltages are applied to the computers of the control system.

The sine-cosine computer 29 solves a triangle having two sides of known magnitude as represented by the voltage inputs ex and ey having a relationship of with respect to one another. The computer obtains from these voltages the azimuth angle and the length of the hypotenuse of the triangle which is the horizontal component of the range to the object. The computer 29 includes a servomotor 35 which operates in response to the voltages ex and ey to rotate its output shaft indicated by the dotted line at 4l to a position indicative of the azimuth angle. A follow-back or null shaft for the computer is driven by the output shaft 4l and is similarly indicated by the dotted line at 4.2. In addition, computer 29 develops a voltage output ehr which is proportional to the hypotenuse of the triangle or the horizontal range to the object.

A dial indicator 43, calibrated in terms of azimuth angle, is attached to output shaft 41, and an azimuth synchro transmitter 44 also has its rotor attached to the output shaft.

Sine-cosine computer 31 performs a similar triangle solving function. It operates on the voltages eh, obtained from computer 29 and the voltage eZ representative of the vertical height component of the object. The cornputer 31 includes a servomotor 37 which operates in response to the voltages ehr and ez to rotate its output shaft indicated by the dotted line 45 to a position indicative of the elevation angle. A follow-back or null shaft for the computer is driven by the output shaft 45 and is similarly indicated by the dotted line at 46. A dial indicator 47, calibrated in terms of elevation angle, is attached to output shaft 45. The rotor of an elevation synchro transmitter is also attached to output shaft 47.

Computer 3l also develops an output voltage er proportional to the hypotenuse of its solved triangle which in this case is the range to the object. Since it is desired to develop the range in terms of a shaft rotation the voltage er is fed as an electrical input to a conventional servo system of the null-balance network type. This servo system is made up or" a servomotor 39. having an output shaft 9, a follow-back or null shaft 50. a source of voltage 53 and a rebalance potentiometer or voltage divider 55. The servomotor 39, responsive to the difference between input voltage e, and the voltage developed across the upper section of the voltage divider 55, will drive its output shaft 49 and through the follow-back or null shaft 50 the slider of voltage divider 55 until these voltages balance or null. At balance. the position of the output shaft 49 will be indicative of the range to the object and the value may be read from a calibrated indicator dial Si attached thereto. A range synchro transmitter 52 is also driven by range output shaft 49.

It will be apparent that it the location of the control system with respect to the director were known in terms of rectangular components, voltages could be applied to the correction terminals proportional to the various coordinate diflerences to correct the system of Fig. l for parallax. The information as to the locations of the two stations is, however, generally known in terms of polar rather than rectangular coordinates. The computation of the proper rectangular coordinate voltages is involved and time consuming. Further, with the polar inforination given in terms of azimuth, elevation and range, a shift in any one of the polar coordinates changes all three of the rectangular coordinates derived therefrom.

The novel circuit of Fig. 2 will allow the setting in of rectangular coordinate corrections directly from polar coordinate data, and the setting of one polar coordinate correction does not disturb any of the other values which have been set previously. This is accomplished by the adoption of a voltage ratio parallax correction circuit which will now be described.

Referring to Fig. 2, the circuit consists of a centertapped source of reference voltage 60 connected across circuit terminals 61 and 62. r[he center-tap o'r` the source t) is connected to ground as indicated. A pair of range voltage dividers or potentiometers 53 and 63' are connected respectively between these terminals and ground. The sliders of the voltage dividers 53 and 63' are mechanically ganged so that they may be adjusted by a common range adjusting knob 65. The movement of the sliders is arranged so that both move outwardly from the ground ends of the dividers on movement of the knob 65. A second pair of voltage dividers 67 and 67 are connected in series across the sliders of the range voltage dividers 63 and 53. The voltage dividers 67 and 67' have a common junction point in that an end or" each is connected to ground. The sliders of voltage dividers 67 and 67' are mechanically ganged to an elevation angle adjustment knob 7i. both sliders moving outwardly from the voltage divider ground tap on movement of the knob. The slider and the ungrounded end of voltage divider 67 are connected through a double pole, double throw, re-

`versing switch 73 to the upper fixed contacts of a pair of single, double throw, switches 75 and 75'. The slider and the ungrounded end of voltage divider 67' are connected through a double pole, double throw, reversing switch 73 to the lower tixed contacts of the switches 75 and 75. Switches 73 and 73' are mechanically ganged. An azimuth angle voltage divider 77 is connected across the upper and lower fixed contacts of switch 75 and its slider is mechanically connected to an azimuth angle adjusting knob 78. .The movable contact of switch 75 and the slider of voltage divider 77 are connected through a double pole, double throw, reversing switch 79 to the output terminals 23 and 25. The movable contact of the switch 75 is connected to the output terminal 27.

The novel correction voltage circuit is connected to the control system of Fig. 7 by connecting its output terminals 23', 25' and 27 to the respective parallax correction terminals 23, 25 and 27 of the input summing amplifiers 11, i3 and l5. The various circuit elements of Pig. 2 have been enclosed iu dotted lines with legends indicative of their function applied thereto. The procedure for setting up correction data will now be described.

Fig. 3 diagrammatically represents a three dimensional system centered about a point O which is the location of the control system of Fig. l. The director or source of data is located at point A and it produces three voltages representative of the position or an object located at point P. The three voltages are in terms of the X, Y and Z components of the point P with respect to point A as a reference. The designation of the components refers to the X, Y and Z axes of the drawing which are located pcrpendicularly to one another.

It will be obvious that data developed by the director at point A as to the location of point P cannot be applied directly at the control system station O. let must be corrected for the difference in position between locations A `and O. The ditterence in location between A and O is determined as by a survey and is usually given in terms or" polar coordinate data, i. e., azimuth angle, elevation Y angle and range. Since the director information is supplied in terms of rectangular rather than polar coordinate form, this location correction ordinarily cannot be ap plied without resolving it into the proper X, Y and Z components. While the resolving operation can be performed mathematically, it is time consuming and the value of the correction cqptponents are interdependent. For example, a change in the elevation angle between stations changes the value of all of the rectangular coordinate correction factors. It is therefore desirable that the parallax correction circuit used be one that will work directly from polar coordinate information without computation, and one where a shift in value of one coordinate of the polar information will not aiect the settings made for the other polar coordinates.

The parallax correction circuit of Fig. 2 constructed in accordance with the invention meets the above requirements. The circuit is set up on a voltage ratio basis such that the setting of any of the polar coordinate inputs does not disturb the setting of the other polar coordinate inputs. Further, the circuit utilizes the computers of the control system of Fig. l to automatically make all the computations necessary to resolve the polar information into rectangular coordinate correction factors.

Assume the correction circuit is set up as shown in Fig. 2 and has its output terminals 23', 25 and 27' connected to the correction terminals 23, 25 and 27 of Fig. l. The director input on terminals 17, i9 and 2l is reduced to zero. The elevation angie magnitude switches 73 and 73 are thrown to their left hand position as shown and the azimuth quadrant switch 75 and the elevation angle quadrant switch 75' are thrown to their upper or (-1-) positions. Azimuth quadrant switch 79 is thrown to the right. The range voltage dividers are set in an arbitrary position which will apply an input voltage to the toilowing components of the system.

The azimuth angle correction is to be made in terms of the ratio between the voltages on terminals 23 and 2S', the X and Y components respectively. The terminal 23' is at the potential of the slider of the range voltage divider 63 and is to serve as the reference potential. The terminalx 25' is connected to the slider of the azimuth angle adjustment voltage divider 77. Starting at the ground point the voltage at terminal 25' can be increased. The azimuth angle indicator 43 will rotate as this voltage is increased up to the point where the slider of voltage divider 77 is at the top and the potential at terminal 25 is equal to that at terminal 23. The azimuth angle indicator at this time will read 45 since the voltages represent the X and Y components of a vector in the first quadrant. To continue sweeping the vector in azimuth, the azimuth quadrant switch 79 is thrown to the left. No change in azimuth dial indication takes place at this time because the potential at terminals 23 and 25 does not change. Terminal 25' now however has the reference voltage applied to it and terminal 23' has a variable voltage. If the slider of voltage divider 77 is now brought down from its maximum positive setting the voltage at terminal 23' drops with respect to the reference potential and the azimuth angle indicator dial continues to rotate from the 45 setting reaching the 90 setting at the time when the slider reaches the ground tap on voltage divider 77. To continue on into the second quadrant the slider need only be moved on past the ground tap to produce negative values at the X correction terminal 23. At maximum negative voltage on terminal 23 the azimuth indicator dial will read 135. Switch 75 is now thrown to the lower or negative position and switch 79 is thrown to the right to establish a negative reference voltage on terminal 23'. The slider of voltage divider 77 is returned to a positive maximum and then reduced to carry the azimuth angle indicator from l to i80. lt is believed that the continued operation of the system covering angles from 180 to 360 will be obvious from the foregoing explanation. Any given polar azimuth angle correction can thus be established by manipulation of the correction circuit while observing the azimuth angle indicator dial 43.

Chee the azimuth angle setting has been obtained the correction circuit is operated to set in the elevationangle correction. The switch 75 is set according to whether the elevation correction angle is positive or negative, i. e., whether the director station is higher or lower than the control system station. It will be remembered that the voltages ex and ey in the computer of Fig. 1 set up a voltage em. which with the voltage ez formed an elevation angle triangle. The correction voltage eh, has been established by setting the azimuth angle correction factors as outlined above.

The established correction voltage eh, is a reference with respect to which the Velevation angle can be set in. The magnitude of eh, being the resultant of ex and ey varies from a minimum at azimuth angles of 0, 90, 180 and 270 to a maximum value midway between these angles. The Z component or voltage is applied to the terminal 27.

Assume the elevation angle correction is positive. Switch 75' is thrown to the upper or (-l-) position. This connects the slider of voltage divider 67 to terminal 27. The slider is moved from the ground end of the voltage divider while watching the elevation angle indicator dial 47 of Fig. l. The elevation angle setting can be increased in this manner until the voltage divider slider is at the upper end. The elevation angle at this time will be somewhere between about 35 and 45 depending upon the magnitude of ehr. lf the desired elevation angle correction should exceed the angle obtainable in this manner the elevation angle magnitude switches 73 and 73 are thrown to the left hand position. This puts the voltage of the sliders of voltage dividers 67 and 67 on the voltage divider 77 and on the terminal 23 or 25' as the reference voltage for the X and Y setting. The X and Y terms having been set in as a ratio are not disturbed with respect to one another although their magnitude and that of the resultant voltage eh, is reduced. The t'ull voltage of the range voltage divider 63 is now applied as a reference' voltage to terminal 27', and the voltage applied to the X and Y terminals 23 and 25' can be reduced to reduce the resultant eh, to increase the setting of the elevation angle. The angle correction can be carried up to in this manner. Obviously negative elevation angle corrections can be set in the same manner by throwing switch 75' to its negative or position.

Unce tne elevation angle is sel in all that remains is the range correction which is accomplished by adjusting the sliders ot the voltage dividers 63 and 63' while observing the range indicator 51. Since both the azimuth angle correction and the elevation angle correction have been set up as voltage ratios, rather than as absolute quantities, the adjustment of the range voltage has no effect upon the azimuth or elevation angle indicators.

It will be apparent that in the light of the above teaching the invention may be practiced by apparatus other than that specifically disclosed herein. It is accordingly to be understood that the invention is not limited to the apparatus shown but is defined solely in terms of the appended claims.

What is claimed is:

l. A parallax correction circuit comprising in combination a pair of input terminals adapted to be connected to a center tapped source of reference voltage, a range adjusting voltage divider means connected to said input terminals, an elevation angle adjusting voltage divider means connected to the outputs of said range adjusting voltage divider means, a pair of single pole, double throw, polarity reversing switches, each switch having a pair of iixed contacts and a movable contact, reversing switch means connecting the outputs of said range adjusting voltage divider means and the outputs of said elevation angle adjusting voltage divider means to the xed terminals of the pair of single pole, double throw, polarity reversing switches, a center-tapped azimuth angle adjusting voltage divider means connected across the tixed contacts of a first one of said single pole, double throw, polarity reversing switches, means including a reversing switch connecting thev output of said azimuth angle adjusting voltage divider means and the movable contact of said firs-1'.' one of said single pole, double throw switches to a pair of output terminals and means connecting the movable contact of the other of said single pole, double throw switches to a third output terminal.

2. ln a parallax correction circuit, a lirst potentiometer means adapted to receive a substantially constant reference voltage potential and for producing two equal and opposite in polarity variable voltages therefrom, a second potentiometer means for receiving said two voltages and for producing equal in magnitude variable outputs from each of said two voltages, a first switching means for receiving one of the voltages from the said first potentiometer means and the portion of the same voltage as supplied through the said second potentiometer means and providing either of these two voltages as an output, a second switching means uni-controlled with said iirst switching means for supplying either the second of said voltages from said rst potentiometer means or the portion of the same voltage as supplied through said second potentiometer means as an output, a third potentiometer means for receiving through said first and second switching means either one of said voltages from said rst potentiometer means and the portion of the opposite voltage from said second potentiometer means and providing a variable choice of output voltage in the range between these received voltages, a third switching means for obtaining an output of either of the two input voltages to said third potentiometer means, three output terminals, a fourth switching means for supplying to a first of said output terminals either of the two voltages from the said S rst and second potentiometer means through said first References Citedin the file of this patent and second switching means which are not oeidg supplied UNH-ED STATES PATENTS to the third potentiometer means, a fth switching means for receiving the output from the said third potentiometer 2447517 Manso Aug' 24' 1948 means and the output of said third switching means and 5 2,391846 Mfm et al- APT- 8 1952 supplying either output to either of a second and third 70611537 White et 31 SePt- 23: 1952 of said output terminals, all of the aforesaid voltages being measured from a common point of reference potential. 

